Reason why is not important but I have 2 D tires and 2 E tires on my truck. They are BFG A/T LT285/70/17. The side wall markings are EXACTLY the same. Both say 3ply polyester,2 ply steel, 1 ply nylon, sidewall 3 plies polyester. Max load single 3195, max load dual 2910. Same number of plies, same load numbers. Only difference is one tire says max load @80psi, the other @ 65psi.
I have about 20k on the tires, both are wearing exactly the same. I rotate every 5k keeping the matching tires on the same axle. I can tell no difference when loaded if the E's or D's are on the back. In the back I run 45 psi empty and 60 loaded, 50 psi in the front always.
.....Oh, and the D's have raised white letters on one side, the E's don't